1. Field of the Invention
The present invention relates in general to a method and apparatus to form a high pressure seal between two wellbore members, and in particular to wickers and an annular sealing ring having an increased rated working pressure.
2. Brief Description of Related Art
In hydrocarbon production wells, a wellhead housing is located at the upper end of the well. The wellhead housing is a large tubular member having an axial bore extending through it. Casing will extend into the well and will be cemented in place. A casing hanger, which is on the upper end of the casing, will land within the wellhead housing. The exterior of the casing hanger is spaced from the bore of the wellhead housing by an annular clearance which provides a pocket for receiving an annulus seal.
There are many types of annulus seals, including rubber, rubber combined with metal, and metal-to-metal. One metal-to-metal seal in use has a U-shape, having inner and outer walls or legs separated from each other by an annular clearance. An energizing ring, which has smooth inner and outer diameters, is pressed into this clearance to force the legs apart to seal in engagement with the bore and with the exterior of the casing hanger.
Some annular seals utilize wickers. Wickers may be located on the exterior of the casing hanger, in the bore of the wellhead housing, or both. The outer leg of the seal embeds into the wickers of the bore while the inner leg of the seal embeds into the wickers of the casing hanger. This locks the annulus seal in place, providing axial restraint, as well as forming a seal.
The sealing wickers are machined directly into the bore of the high pressure housing and landing subs or the neck of the casing hangers. The annulus seal is made of a sufficiently deformable metal to allow it to deform against the wickers of the casing hanger. The deformation occurs as the wickers “bite” into the annulus seal. In order to cause the seal to deform without damaging the wickers, the annulus seal is made of a metal that is softer than the steel used for the casing hangers.